The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Compression ignition (CI) engines include diesel engines and homogenous charge compression ignition (HCCI) engines. In CI engines, a piston compresses an air/fuel (A/F) mixture in a cylinder to combust the A/F mixture. Typically, a constant amount of air is drawn into a CI engine (as opposed to a throttled air intake in a spark-ignition engine). In other words, the A/F mixture in a CI engine (and thus the output power) is controlled by the amount of fuel that is injected.
In addition to a different combustion process, CI engine systems also use different types of fuel. Cetane number (CN) is a measurement of the ignition or combustion quality of CI fuel during compression ignition. In particular, CN affects an ignition delay of CI fuel. The ignition delay is defined as the time period between the start of injection of fuel into a CI engine and the start of combustion of the A/F mixture in the CI engine. CI fuels with higher CNs tend to have shorter ignition delays (and therefore less time for the A/F mixture to form) than CI fuels with lower CNs.
CI fuel may be found with a wide range of CNs. For example, different countries require different minimum CNs. CI fuel quality at different service stations may also vary. Operating a CI engine on CI fuel with a different CN than it is calibrated for may adversely affect, for example, combustion efficiency, exhaust pressure, boost pressure, exhaust gas recirculation (EGR), A/F ratio, emissions, and/or noise/vibration/harshness (NVH).